1. Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus characterized by its zoom mechanism.
2. Description of the Related Art
Conventionally, there have been proposed various techniques concerning a zoom lens barrel which is extended from the body of an image pickup apparatus for shooting and retracted into the apparatus body for accommodation. This type of zoom lens barrel is formed by combining a plurality of rectilinear motion barrels and rotary barrels, and is configured to be advanced and retracted along an optical axis direction. Further, when the image pickup apparatus is not in use, these barrels are retracted, whereby the thickness of the main unit of the image pickup apparatus is reduced.
In such a retractable lens barrel, when cams are formed in cam barrels, it is required to lay out the respective shapes of cams such that they do not interfere with each other. Further, it is required to provide a rectilinear motion guide in each of lens units.
In a lens barrel mechanism disclosed in Japanese Patent No. 3842087, a rotary barrel is formed with cams on outer and inner surfaces thereof such that the cams do not cross each other. Therefore, without providing a dedicated cam barrel for each of lens units, it is possible to move each lens unit in an optical axis direction using the single rotary barrel which is short in length. Further, rectilinear motion barrels for rectilinearly guiding the lens units, respectively, are rectilinearly guided by a fixed barrel, and hence they are not required to be engaged with each other. This contributes to reduction of the size of the lens barrel mechanism.
In a lens barrel formed by a combination of cam barrels and rectilinear motion barrels, including the lens barrel mechanism disclosed in Japanese Patent No. 3842087, generally, each cam barrel and each rectilinear motion barrel associated therewith are caused to move in unison in the optical axis direction. To cause the cam barrel and the rectilinear motion barrel to move in unison in the optical axis direction, in the above-described example, a projection is formed on one of the barrels and a groove is formed on the other, for example, whereby the two are caused to move in unison when they come to a predetermined phase. By providing such a so-called bayonet mechanism, the cam barrel and the rectilinear motion barrel are caused to move in unison in the optical axis direction.
However, this mechanism prevents cams from being laid out in a manner extending across the surface of the cam barrel, which is a hindrance to the reduction of the size of the lens barrel in the optical axis direction.
Further, in the lens barrel mechanism disclosed in Japanese Patent No. 3842087, the rectilinear motion barrels for rectilinearly guiding the lens units, respectively, are rectilinearly guided by the fixed barrel independently of each other. However, since the lens units are guided by the respective linear motion barrels which are independent of each other, it is difficult to maintain the accuracy of rectilinear guidance between the lenses.